Light-emitting device

ABSTRACT

In a first aspect of the present inventive subject matter, a light-emitting device includes a magnetic circuit including a magnetic gap; a movable member including a coil that is electrically connectable to an alternating current power source and arranged in the magnetic gap of the magnetic circuit; and a light source including a light-emitting diode and arranged above the movable member, and the movable member is able to be activated with a voltage falling in a range of one to five percent of an entire voltage range that is applicable to the light-emitting device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a new U.S. patent application that claims benefit ofU.S. provisional application No. 62/118,651, filed on Feb. 20, 2015, thedisclosures of which are incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a light-emitting device including alight source that includes a light-emitting diode (LED), and relates toa light-emitting device including a heat-releasing structure.

Description of the Related Art

A light-emitting device including an LED and a heat-releasing structureis known to the public.

For example, it is open to the public that a light-emitting deviceincludes a base made of a metallic material and light-emitting diodes(LEDs) thermally connected to the base (For reference, see U.S.Unexamined Patent Application Publication No. 2009/0160302 A1).

Also, it is open to the public that a lamp includes an air-cooling unitincluding a motor and a fan that is rotary-driven by the motor (Forreference, see U.S. Unexamined Patent Application Publication No.2010/0026185 A1).

SUMMARY OF THE INVENTION

In a first aspect of the present inventive subject matter, alight-emitting device includes a magnetic circuit including a magneticgap; a movable member including a coil that is electrically connectableto an alternating current power source and arranged in the magnetic gapof the magnetic circuit; and a light source including a light-emittingdiode and arranged above the movable member, and the movable member isable to be activated with a voltage falling in a range of one to fivepercent of an entire voltage range that is applicable to thelight-emitting device.

In a second aspect of the present inventive subject matter, alight-emitting device includes a casing including an opening; alightsource supported by the casing; an air passage arranged adjacent to thelight source; a magnetic circuit including a yoke, a permanent magnetarranged in contact with the yoke, a top plate arranged on the permanentmagnet to form a magnetic gap between the top plate and the yoke; and amovable member being positioned below the light source in the casing andincluding a coil that is arranged in a magnetic gap.

In a third aspect of the present inventive subject matter, alight-emitting device includes a magnetic circuit including a yoke, apermanent magnet arranged in contact with the yoke, and a top platearranged on the permanent magnet to form a magnetic gap between the topplate and the yoke; a movable member including a coil to which analternating current is supplied when the light-emitting device isactivated; a rectifier to which the alternating current is supplied whenthe light-emitting device is activated; and a light source to which arectified current rectified from the alternating current by therectifier is supplied when the light-emitting device is activated, thecoil of the movable member to which the alternating current isconfigured to be supplied before the alternating current is supplied tothe rectifier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a top plan view of a light-emitting device as anembodiment of the present invention.

FIG. 1B shows a top plan view of the light-emitting device shown in FIG.1A, with a light-transmitting cover removed.

FIG. 1C shows a side view of a light-emitting device as an embodiment ofthe present invention.

FIG. 1D is a cross-sectional view of a light-emitting device as anembodiment of the present invention, taken along a dotted and dashedline ID-ID shown in FIG. 1A.

FIG. 2A shows a top plan view of a movable member of a light-emittingdevice according to an embodiment of the present invention.

FIG. 2B is a cross-sectional view of a movable member arranged in amagnetic gap of a magnetic circuit, and taken along a dotted and dashedline IIB-IIB shown in FIG. 2A.

FIG. 2C is a partially enlarged cross-sectional view of a coil, shown ina dotted elliptic circle in FIG. 2B.

FIG. 3 shows a circuit diagram for a light-emitting device according toan embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the subjectmatter. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise.

As illustrated in the figures submitted herewith, some sizes ofstructures or portions may be exaggerated relative to other structuresor portions for illustrative purposes. Relative terms such as “below” or“above” or “upper” or “lower” may be used herein to describe arelationship of one element, layer or region to another element, layeror region as illustrated in the figures. It will be understood thatthese terms are intended to encompass different orientations of a devicein addition to the orientation depicted in the figures.

Embodiments of the invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.

Embodiments of the invention are described with reference to drawingsincluded herewith. Same and/or similar reference numbers refer to sameand/or similar and/or corresponding and/or related structuresthroughout. It should be noted that the drawings are schematic innature.

FIG. 1D is a cross-sectional view of a light-emitting device as anembodiment of the present invention, taken along a dotted and dashedline ID-ID shown in FIG. 1A.

FIG. 2B is a cross-sectional view of a movable member arranged in amagnetic gap of a magnetic circuit, and taken along a dotted and dashedline IIB-IIB shown in FIG. 2A.

According to an embodiment of a light-emitting device of the subjectinvention, the light-emitting device 100 includes a magnetic circuit 22including a magnetic gap 22 a; a movable member 2 including a coil 12that is electrically connectable to an alternating current (AC) powersource and arranged in the magnetic gap 22 a of the magnetic circuit 22;and a light source 4 including an LED and arranged above the movablemember 2.

In an alternating current (AC), the flow of electric charge periodicallyreverses direction. AC is the form in which electric power is deliveredto businesses and residences, and thus, an alternating current powersource 1 is positioned outside of the light-emitting device 100.

The movable member 2 is able to be activated with a voltage that isapplied to the coil 12. The voltage that is applicable to the coil 12may fall in a range of one to five percent of an entire voltage rangeapplicable to the light-emitting device 100. Accordingly, the movablemember 2 with the coil 12 arranged in the magnetic gap 22 a of themagnetic circuit 22 is able to be activated by a comparatively smallvoltage range in an entire voltage range to the light-emitting device.

FIG. 3 shows a circuit diagram for a light-emitting device according toan embodiment of the present invention.

The light-emitting device 100 may further include a rectifier 3 that iselectrically connectable to an AC power source 1. The rectifier 3 isconfigured to rectify an AC originating from the AC power source 1 tosupply a rectified current to the light source 4. The light-emittingdevice 100 may include parts that include a fuse 5 and a varistor 6. Afuse is a device used in an electrical device and/or system to protectagainst an excessive current. A varistor is an electronic component withan electrical resistivity that varies with a voltage applied.

Also, the reference number 5 shown in FIG. 3 is a fuse.

FIG. 2A shows a top plan view of a movable member of a light-emittingdevice according to an embodiment of the present invention.

The movable member 2 may further include a panel 16 arranged on the coil12. The word “panel” here includes a diaphragm. The magnetic circuit 22may include a yoke 15, a permanent magnet 14 arranged on the yoke 15,and a top plate 17 arranged on the permanent magnet 14 to form amagnetic gap 22 a between the top plate 17 and the yoke 15. Thepermanent magnet 14 may be arranged in a recessed portion 15 a of theyoke 15, and a lower portion of the permanent magnet 14 is in contactwith the yoke 15.

FIG. 1C shows a side view of a light-emitting device as an embodiment ofthe present invention.

As shown in FIG. 1D that is a cross-sectional view of a light-emittingdevice, the light-emitting device 100 may further include a casing 11that includes an opening 11 a. The light source 4 may be positioned atthe opening 11 a above the movable member 2 that is arranged in thecasing 11. The light source 4 may be positioned to close the opening 11a above the movable member 2 that is arranged in the casing 11.

Namely, the coil 12 of the movable member 2 is arranged in the magneticgap 22 a of the magnetic circuit 22, which is arranged in the casing 11at a position lower than a position of the movable member 2. The lightsource 4 may be directly supported by the casing 11. The light source 4includes a substrate 7 to which the LED is electrically connected. Anouter surface of the casing 11 may be covered by anelectrically-insulating layer 18 as shown in FIG. 1C.

If the number of LEDs arranged in a light source 4 increases and/or thesize of each LED increases, the light source and/or a light-emittingdevice including the light source require a heat-releasing structure torelease heat from the LEDs. The casing 11 may be made of metallicmaterial and thermally connected to the light source 4. The substrate 7may be a ceramic substrate. The substrate 7 may include a metal plateand/or a heatsink that is thermally connected to the LED and to thecasing 11. The substrate 7 may include an electrically-insulating layerthat is made of a resin.

Also, the light source 4 may be supported by the casing 11 through ametal plate 7′ and/or a heatsink that is additionally arranged.

Furthermore, an air passage 10 may be arranged at a position below thelight source 4 and above the panel 16 of the movable member 2. The airpassage 10 may be arranged adjacent to the light source 4 to releaseheat generated in the light source 4 efficiently. The casing 11 mayinclude an air passage 10 at a peripheral side portion of the casing 11.

The up and down movement of the coil 12 conform to up and down shapes ofAC waveform. When the coil 12 on which the panel 16 is arranged is at ahigher position as an up position, the movable member 2 pushes airheated by the light source 4 in the casing 11 toward outside of thecasing 11 of the light-emitting device 100. When the coil 12 on whichthe panel 16 is arranged is at a lower position as a down position, themovable member 2 introduces air from outside of the casing 11 of thelight-emitting device 100 into a space in the casing 11. Accordingly,the heated air in the casing 11 is able to be circulated to cool downthe light source 4 in the light-emitting device 100.

A light-emitting device according to an embodiment of the presentinvention includes means for circulating air that is heated by a lightsource when the light source is activated; means for flowing alternatingcurrent through a coil of a movable member; and means for flowingrectified current through the light source.

FIG. 1A shows a top plan view of a light-emitting device as anembodiment of a light-emitting device.

FIG. 1B shows a top plan view of the light-emitting device shown in FIG.1A, with a light-transmitting cover 20 removed. The light-transmittingcover 20 may be a lens. Also, the light-transmitting cover may include acurving shape.

FIG. 1C shows a side view of light-emitting device as an embodiment ofthe subject matter.

FIG. 1D is a cross-sectional view of light-emitting device, taken alonga dotted and dashed line ID-ID shown in FIG. 1A. The air passage 10 maybe positioned below the light source 4 and above the panel 16 of themovable member 2.

According to an embodiment of a light-emitting device of the presentinvention, a light-emitting device 100 may include a casing 11 includingan opening 11 a; a light source 4 that is supported by the casing 11.The light source 4 may be supported by an upper stepped portion of thecasing 11. The light-emitting device 100 may further include a magneticcircuit 22 including a yoke 15, a permanent magnet 14 arranged incontact with the yoke 15, a top plate 17 arranged on the permanentmagnet 14 to form a magnetic gap 22 a between the top plate 17 and theyoke 15. The light-emitting device 100 may further include a movablemember 2 that is positioned below the light source 4 in the casing 11and includes a coil 12 arranged in a magnetic gap 22 a between the topplate 17 and the yoke 15. The movable member 2 of the light-emittingdevice 100 may further include a panel 16 arranged on the coil 12. Thelight source 4 may include LEDs that are arranged in an area positionedabove the panel 16 of the movable member 2. The permanent magnet 14 maybe arranged in a recessed portion 15 a of the yoke 15.

When the light-emitting device 100 is activated, the coil 12 of themovable member to which a part of AC is supplied will be activated. Themovable member 2 is included in the light-emitting device. The movablemember 2 is able to be activated by a small voltage of about 3 to 5volts, for example. The AC except a part of the AC supplied to the coil12 may be rectified by the rectifier 3 to supply a rectified current tothe light source 4.

The movable member 2 includes a coil 12. The coil 12 includes a wire 12b winding around a bobbin 12 a. AC is configured to be supplied to thecoil 12 of the movable member 2 before being supplied to the rectifier3.

The coil 12 of the movable member 2 is electrically positioned betweenan AC power source and the rectifier 3. The rectifier 3 may convert AC,which periodically reverses direction, to a rectified current, whichflows in only one direction.

For more details about the magnetic gap 22 a, the magnetic gap 22 a isformed between a periphery of the top plate 17 and an upper portion ofthe yoke 15. The movable member 2 includes a coil 12, which includes abobbin 12 a and a wire 12 b winding around the bobbin 12 a. The movablemember 2 may include an FPC (flexible printed circuit) 23. The FPC 23may be partly attached to the movable member 2. Of course, thearrangement of an FPC 23 is not limited to an arrangement shown in FIG.2A.

The light-emitting device 100 may further include a base 19 thatincludes a first terminal 19 a and a second terminal 19 b. FIG. 1C showsthe first terminal 19 a and the second terminal 19 b as pins. Also, thebase 19 may be a screw base instead of pins. The shape of the base 19may be various shapes compatible to sockets which are already known andused.

As shown in FIG. 1B, a light source 4 includes a substrate 7. The lightsource 4 may include LEDs that are electrically arranged in seriesand/or in parallel to at least a pair of electrodes arranged on thesubstrate. A first electrode 8 a arranged on a substrate 7 of the lightsource 4 may be electrically connected to a first electrode of therectifier 3 by a first lead wire 9 a. A second electrode 8 b arranged onthe substrate 7 of the light source 4 may be electrically connected to asecond electrode of the rectifier 3 by a second lead wire 9 b.

The first lead wire 9 a may be soldered on the first electrode 8 a ofthe light source at one end of the first lead wire 9 a. The second leadwire 9 b may be soldered on the second electrode 8 b of the light source4 at one end of the second lead wire. The rectifier 3 may beelectrically connected to the coil 12 of the movable member 2, an ACpower source 1, and the light source 4. The rectifier 3 may be a bridgerectifier.

The substrate 7 may be a resin substrate. The substrate 7 may include ametal plate 7′ to which the LEDs are thermally connected. The substrate7 may be a ceramic substrate.

According to an embodiment of the present invention, a light-emittingdevice including: a magnetic circuit 22 that includes a yoke 15, apermanent magnet 14 arranged in contact with the yoke 15, and a topplate 17 arranged on the permanent magnet 14 to form a magnetic gap 22 abetween the top plate 17 and the yoke 15; a movable member 2 including acoil 12 that is electrically connectable to an AC power source 1 suchthat AC from the AC power source flows through the coil 12 of themovable member 2; a rectifier 3 electrically connected to the AC powersource 1; and a light source 4 electrically connected to the rectifier 3such that a rectified current that originates from the AC and isrectified by the rectifier 3 flows through the light source 4.

The movable member 2 herein moves repeatedly up and down when AC flowsthrough the movable member. When the AC power source 1 to activate thelight-emitting device 100 is switched on, AC from the AC power source 1flows through the coil 12 of the movable member 2, and AC is rectifiedby the rectifier 3 to be a rectified current. Then, the rectifiedcurrent is configured to flow through the light source 4 that includesLEDs to emit light.

Accordingly, a magnetic force produced in the magnetic gap 22 a movesthe coil 12 with a panel 16 up and down. The up and down movement of thecoil 12 conform to up and down shapes of AC waveform. When the coil 12on which the panel 16 is arranged is at a higher position, the movablemember 2 pushes air heated by the light source 4 in the casing 11 towardoutside of the casing 11 of the light-emitting device 100. When the coil12 on which the panel 16 is arranged is at a lower position, the movablemember 2 introduces fresh air outside of the casing 11 of thelight-emitting device 100 into a space in the casing 11. Accordingly,the heated air in the casing 11 is able to be circulated.

The air circulation in a space below the light source allows the lightsource to cool down when the light-emitting device is activated. Itrequires a small voltage to activate the movable member 2 to circulateair in this embodiment of the light-emitting device. For example, thesmall voltage can be around 3-5 volts. A voltage of around 220-230 voltsand a frequency of 50 cycles per second are used in Europe, most ofAsia, most of South America and Australia, for example.

Accordingly, the required voltage to activate the movable member in thisembodiment is comparatively small to an entire amount of voltage, andwith such a small voltage, the light source of the light-emitting devicecan be cooled down. In other words, the movable member 2 is able to beactivated with a voltage falling in a range of one to five percent of anentire amount of voltage that is applicable to the light-emittingdevice.

Also, as another embodiment, it is possible to arrange two coils thatare opposite in phase. Operating sound of the coils in a movable membermay be restrained or canceled by each other of the two coils that areopposite in phase.

According to an embodiment of the subject matter, a light-emittingdevice 100 includes a casing 11 includes an opening; a light source 4supported by the casing 11; an air passage 10 arranged adjacent to thelight source 4; a magnetic circuit 22 including a yoke 15, a permanentmagnet 14 arranged in contact with the yoke 15, a top plate 17 arrangedon the permanent magnet 14 to form a magnetic gap 22 a between the topplate 17 and the yoke 15; and a movable member 2 being positioned belowthe light source 4 in the casing 11 and including a coil 12 that isarranged in a magnetic gap 22 a.

The air passage 10 connects an inside space of the casing 11 and anoutside of the casing 11. If the air passage 10 is arranged adjacent tothe light source 4, it is possible to circulate heated air by the lightsource 4 in the casing 11 and fresh air outside the casing 11effectively. If a surface area of the air passage 10 becomes larger,heat-releasing effect of heated air may increase. Accordingly, it ispossible to increase the surface area of the air passage to have a shapeof slit as shown in FIG. 1C. Also, two or more air passages 10 may bearranged through the casing 11 adjacent to the light source 4. The airpassage 10 may be a groove, an opening and/or a hole. With a smalleropening and/or a hole, air in the casing 11 may be circulated in afaster speed with the movement of the movable member 2.

FIG. 2C is a partially enlarged cross-sectional view of a coil, shown ina dotted elliptic circle in FIG. 2B.

As shown in FIG. 2B and FIG. 2C, it is possible to arrange a magneticfluid 13 arranged on an outer peripheral side of the coil 12 of themovable member 2. The magnetic fluid 13 on the outer peripheral side ofthe coil 12 is drawn to the coil 12 in the magnetic gap 22 a formedbetween the top plate 17 and the yoke 15. Accordingly, the magneticfluid 13 on the outer peripheral side of the coil 12 holds the coil in aposition to allow the coil to start to move and/or continue to move upand down, when the light-emitting device 100 is activated. The coil 12may include a bobbin 12 a, and the number of turns of winding wire 12 bof the coil 12 around an upper portion, which is shown as a dotted arrow“a” in FIG. 2C, of the bobbin 12 a is more than the number of turns of awinding wire 12 b of the coil 12 around a middle portion, which is shownas a dotted arrow “b” in FIG. 2C, of the bobbin 12 a in both directionsof the up and down movement of the coil shown as the both directionsarrow in FIG. 2B. The number of turns of the winding wire 12 b of thecoil 12 around a lower portion, which is shown as a dotted arrow “c”, ofthe bobbin 12 a is more than the number of turns of the winding wire 12b of the coil 12 around the middle portion “b” of the bobbin 12 a in theboth directions of the up and down movement of the coil 12. Thisconfiguration may be useful for the magnetic fluid 13 on the outerperipheral side of the coil 12 to hold the coil in a position to allowthe coil to start to move and/or continue to move up and down, when thelight-emitting device 100 is activated. Even if the light-emittingdevice 100 is turned off, the coil with the magnetic fluid 13 may beable to return to a neutral position from which the coil is able to movewhen the light-emitting device 100 is turned on.

In addition, as an embodiment of the subject matter, the middle portion“b” of the bobbin 12 a may be exposed from the winding wire 12 b of thecoil 12. The magnetic fluid 13 may be positioned on the middle portionof the bobbin 12 a.

FIG. 3 shows a circuit diagram for a light-emitting device according toan embodiment of the subject matter. The reference number 1 in FIG. 3shows an alternating current (AC) power source. In alternating current(AC), the flow of electric charge periodically reverses direction. AC isthe form in which electric power is delivered to businesses andresidences, and thus, the AC power source 1 is positioned outside of thelight-emitting device. The movable member 2 includes a coil 12, to whichan AC is supplied when the light-emitting device 100 is activated. Also,the light-emitting device 100 may include the rectifier 3, to which thealternating current is supplied when the light-emitting device 100 isactivated. The light-emitting device 100 may include a light source 4,to which a rectified current rectified from the alternating current bythe rectifier 3 is supplied when the light-emitting device 100 isactivated. The alternating current is configured to be supplied to thecoil 12 of the movable member 2 before being supplied to the rectifier3.

Furthermore, while certain embodiments of the present inventive subjectmatter have been illustrated with reference to specific combinations ofelements, various other combinations may also be provided withoutdeparting from the teachings of the present inventive subject matter.Thus, the present inventive subject matter should not be construed asbeing limited to the particular exemplary embodiments described hereinand illustrated in the Figures, but may also encompass combinations ofelements of the various illustrated embodiments.

Many alterations and modifications may be made by those having ordinaryskill in the art, given the benefit of the present disclosure, withoutdeparting from the spirit and scope of the inventive subject matter.Therefore, it must be understood that the illustrated embodiments havebeen set forth only for the purposes of example, and that it should notbe taken as limiting the inventive subject matter as defined by thefollowing claims. The following claims are, therefore, to be read toinclude not only the combination of elements which are literally setforth but all equivalent elements for performing substantially the samefunction in substantially the same way to obtain substantially the sameresult. The claims are thus to be understood to include what isspecifically illustrated and described above, what is conceptuallyequivalent, and also what incorporates the essential idea of theinventive subject matter.

What is claimed is:
 1. A light-emitting device comprising: a casingcomprising an opening; a magnetic circuit comprising a magnetic gap; amovable member comprising a coil that is electrically connectable to analternating current power source and arranged in the magnetic gap of themagnetic circuit; and a light source comprising a light-emitting diodeand arranged above the movable member, wherein the light source ispositioned to close the opening above the movable member that isarranged in the casing, and wherein the movable member is able to beactivated with a voltage falling in a range of one to five percent of anentire voltage range that is applicable to the light-emitting device. 2.The light-emitting device according to claim 1, further comprising: arectifier that is electrically connectable to the alternating currentpower source, wherein the light source is electrically connected to therectifier, and the rectifier is configured to rectify an alternatingcurrent originating from the alternating current power source to supplya rectified current to the light source.
 3. The light-emitting deviceaccording to claim 1, wherein the movable member further comprises apanel arranged on the coil.
 4. The light-emitting device according toclaim 1, wherein the magnetic circuit comprises a yoke, a permanentmagnet arranged in a recessed portion of the yoke, and a top platearranged on the permanent magnet to form the magnetic gap between thetop plate and the yoke.
 5. The light-emitting device according to claim3, further comprising: an air passage arranged below the light sourceand above the panel of the movable member.
 6. A light-emitting devicecomprising: a magnetic circuit comprising a magnetic gap; a movablemember comprising a coil that is electrically connectable to analternating current power source and arranged in the magnetic gap of themagnetic circuit; a light source comprising a light-emitting diode andarranged above the movable member; and a magnetic fluid arranged on anouter peripheral side of the coil of the movable member, wherein themovable member is able to be activated with a voltage falling in a rangeof one to five percent of an entire voltage range that is applicable tothe light-emitting device.
 7. A light-emitting device comprising: amagnetic circuit comprising a magnetic gap; a movable member comprisinga coil that is electrically connectable to an alternating current powersource and arranged in the magnetic gap of the magnetic circuit; and alight source comprising a light-emitting diode and arranged above themovable member, wherein the movable member is able to be activated witha voltage falling in a range of one to five percent of an entire voltagerange that is applicable to the light-emitting device, wherein the coilcomprises a bobbin and a winding wire, a number of turns of the windingwire of the coil around an upper portion of the bobbin being more than anumber of turns of the winding wire of the coil around a middle portionof the bobbin in a direction of up and down movement of the coil, andwherein a number of turns of the winding wire of the coil around a lowerportion of the bobbin is more than the number of turns of the windingwire of the coil around the middle portion of the bobbin in thedirection of up and down movement of the coil.
 8. The light-emittingdevice according to claim 7, further comprising: a magnetic fluid,wherein the middle portion of the bobbin is exposed from the windingwire of the coil, and the magnetic fluid is positioned on the middleportion of the bobbin.
 9. A light-emitting device comprising: a casingcomprising an opening; a light source supported by the casing; an airpassage arranged adjacent to the light source; a magnetic circuitcomprising a yoke, a permanent magnet arranged in contact with the yoke,a top plate arranged on the permanent magnet to form a magnetic gapbetween the top plate and the yoke; a movable member positioned belowthe light source in the casing and comprising a coil that is arranged inthe magnetic gap; and a magnetic fluid arranged on an outer peripheralside of the coil of the movable member.
 10. The light-emitting deviceaccording to claim 9, wherein the coil comprises a bobbin and a windingwire, a number of turns of the winding wire of the coil around an upperportion of the bobbin being more than a number of turns of the windingwire of the coil around a middle portion of the bobbin in a direction ofup and down movement of the coil.
 11. The light-emitting deviceaccording to claim 9, wherein the coil comprises a bobbin and a windingwire, and wherein a middle portion of the bobbin is exposed from thewinding wire of the coil, and the magnetic fluid is positioned on themiddle portion of the bobbin.
 12. The light-emitting device according toclaim 9, wherein the movable member is able to be activated with avoltage falling in a range of one to five percent of an entire amount ofvoltage that is applicable to the light-emitting device.
 13. Alight-emitting device comprising: a magnetic circuit comprising a yoke,a permanent magnet arranged in contact with the yoke, and a top platearranged on the permanent magnet to form a magnetic gap between the topplate and the yoke; a movable member comprising a coil to which analternating current is supplied when the light-emitting device isactivated; a rectifier to which the alternating current is supplied whenthe light-emitting device is activated; and a light source to which arectified current rectified from the alternating current by therectifier is supplied when the light-emitting device is activated,wherein the coil of the movable member is configured to be supplied thealternating current before the alternating current is supplied to therectifier, and wherein the coil of the movable member is electricallypositioned between an alternating current power source and therectifier.
 14. The light-emitting device according to claim 13, whereina first electrode of the light source is electrically connected to afirst electrode of the rectifier, and a second electrode of the lightsource is electrically connected to a second electrode of the rectifier.15. The light-emitting device according to claim 13, wherein therectifier is electrically connected to the coil of the movable member,the alternating current power source, and the light source.
 16. Thelight-emitting device according to claim 13, wherein the rectifier is abridge rectifier.
 17. The light-emitting device according to claim 13,wherein the movable member is able to be activated with a voltagefalling in a range of one to five percent of an entire amount of voltagethat is applicable to the light-emitting device.